Refactoring of some tests, added new physics and rendering tests

Sky sphere test tests the rendering of the skybox.

Terrain sky sphere test tests the rendering of the skybox behind the
terrain sphere

Bullet physics terrain test loads and simulates the sphere terrain mesh.
This test also has ray casting and picking as well as the skybox
rendering integrated.

Terrain segment has been seperated out and has updated UV mapping to
work properly with cubemaps exported from Spacescape.